Automatic trunking system.



A. E. KEITH. AITOMATICv TRUNKlNG SYSTEM.

APPLIATION FILED MAE.. 1, 1910.

.Patented June 3G, 1914.

8 SHEETS-SHEET l.

f fA. E. KEER. AUTOMTIG `TVRUNKNG SYSTEM. APPLICATION FILED MAB.. 1*, 19,10.

A..E. KEITH. AUTOMATIC TRUNKING SYSTEM. APPLICATION FILED MAR. 1. 1910.

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e SHEETS-SHEET s.

M/TESSES @f @my Patented June 30, 191i fw@ GROUP THUN/ 5 Patented June 30, 1914 APPLICATION FILED HAL-1. 1910 v ,WIT/VESSES A, E. KEITH. AUTOMATIC TRUNKING SYSTEM.

APPLICATION FILED MARA, 1910.

.' Patented June 30,1914.

W//VESSS A.. E. KEITH. AUTOMATIC TRUNKING SYSTEM. APPLIGATION FILED M1111, 1910.

6 SHEETS-SHEET 6.

W/WVESSES Q URW-i Patented June 30, 1914 PEL/775 //V SECO/VDHY /W/STESW/TCH rien ALEXANDER E. KEITH, OF HINSDALE, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, 0F CHICAGO, ILLINOIS, Al CORPORATION OF ILLINOIS.

AUTOMATIC TRUNKING SYSTEM.

meeste.

Specification of Letters Patent.

Patented J une 3), 191e.

Application ated March 1 i910. serial no. 546,616;

To all whomit m @y concern Be it known that I, ALEXANDER E. Knrrn, a citizen of the United States of America, and resident of Hinsdale, Dopage county, Illinois, have invented a certain new and useful Improvement in Automatic rTrunking Systems, of which the 'following is a specification. .1

My invention relates to automatic or semiautomatic telephone exchange systems ot' that kind in which each subseribers line is provided with a non-numerical 'trunking switch, and in which the trunks leading from these individual or line switches terminate in secondary line switches, whereby at least t-wo non-numerical trunking operations occur betiire the call reaches the first selector or other switching apparatus. In a system of this kind the primary or subscribers individual line switches are arranged in groups, and the said secondary line switches are also arranged in groups, the -tirst comprising, say, ten groups and the second ten groups. As heretofore, constructed, it was found that the secondary line switches of agroup were liable to be put in use one at a time, until all trunks, leading from that group were in use, before any ot the calls coming through any oit the groups of primary line switches would be directed to another group ot' secondary line switches. In other words, it was 'found that the calls Jfrom the diti'erent groups ot suhscrihers would, in many cases, be taken -are of bya certain group of secondary line switches, and that this group would till up,

to speak, so that the trunks leading therefrom would all be put in use before subsequent calls would be taken care ot' by the other groups ot secondary line switches. In this way the load was not evenly di--tributed between the groups ol' steondary line switches` as the first group was quite liable to be subjected to a heavier load than the others, and consequently the wear and tear on the apparatus was not evenly distributed between all parts thereof. It will be understood, of course, that successive calls coming from the same group ot' subscribers would be distributed between diterent grotups ot secondary line switches. The trouble, however, was that successive calls coming from different groups of subscribers would all be concentrated, so to speak in a certain group ei secondary line switches.

rl`he object ofrmy invention is, therefore, to provide a system in which primary and secondary 'line switches are used, and in which provision is made whereby the load or traffic is at all times evenly distributed between the ditl'erent groups of secondary line switches, thus making it possible, and practically the rule, for example, for a subscriber of one group to call through and obtain connection with a secondary switch in the rst group, and for a subscriber of an other group to then call through and obtain connection with a secondary switch in the second group, even though the trunks leading from the first secondary group are not all busy. This means, ot course, that the trunks leading from a certain group of primary line switches are ldistributed between the diil'erent groups of secondary liuc switches, and that the master switchesI for the ditl'erent groups of primary line switches, or some ot them, are so constructed and operated that each master switch is in selective relation to a diti'erent group of secondary liuc switches, even though the master switches, or some et them, are all in the same position. Consequently, as stated, a subscriber in the first group may call and obtain connection with a secondary line switch in one group; then a subscriber in the second group may call and automatically obtain connection with a secondary line switch in another group, even though the trunks leading trom they group receiving the tirst call are not all busy; and subscribers successively calling troni other groups are. in a similar manner. given connection with :secondary line switches in as many ditl'erent groups. \\'ith the oh. method there was unich more likely to be a single preselected group ot secondary switches in readiness for the groups ol' subscribers. and the tirst calling subscriber would get this group, regardless ot which group otprimary,switches the call came trom. Now. however, with my improved arrangement there is more likt-I",v to be a preselected `group in readiness for cach group ot subscribers-that is' to say, a different group of secondary switches for each group ot subscribers, whereby a subscriber calling trom one group will get a preselected trunk leading to one group ol secondary line switches, and the subscriber calling :troni another group will get another preselected trunk leading to another group of secondary line switches. "lhus, the load is evenly distributed between the dillerent groups of secondary line switches, and the liability of concentration 'of a number ol calls in one group of such Switches is re duced to a minimum.

In the accompanying drawings Figures l, 2 and 3 taken together show the complete connections between a calling substation A (Fig. l) and a called substation A2 (llig. 3) in a system embodying the principles el :my invention. Fig. 4r is a table showing the distribution of the trunks between the pri* mary and secondary line switches. Fig. 5 is a simplified diagram ol the trunlring bctween the primary and secondary switches, the trunks being distributed according to the table shown in 4l. Fig. 6 shows diay gralninatleallythe'connections between the fill auxiliary banks of master switches of the primary line switches.

To the substation A. (Fig. 1) there is allotted the individual or line switch C. rl`his line switch C,`together with a number ol other similar switches, is controlled by a common mechanism .D usually called a inaster switch. Accessible to the line switch C is a group of trunk lines leading to secondary line switches C. Accessible to the secondary switch Cfis the numerical switch E '(lllig.A 2), commonly called a first selector.

The lirstselector E is one oit a group of selectors common to a. group of secoiulary switches C. At F is shown a .so-called second selector which is one ola number of solector-s common and accessible to a number of first selectors E. At lvl (llig. 3) is shown a "connector switch by means of which connection may be completed 4to any one of a Agroup of substations of which substation A2 is a member.

The substation iig provided with a line switch C2 similar to the line switch C of substation A. At l shown a busy signaling machine, and at lli a. ringing current generator is shown.

The automatic substations may be of any suitable or approved type. As here shown. the substation A comprises areceiver Q0, switch hook 21, impulse wheel 22, transmitter 23, induction coil 24, ringer 25, condenser 26 and impulse springs 27 and 28. The switch hook controls the substation circuits through the medium ol the cam arm 29 and springs 305 3l and 32. "When the receiver is on the hook the arno 29 maintains the spring 3l in Contact with the springv 32,

vthus bridging the .rin erfl and condenser 26 in series across the ine conductors 33 and :34. When the receiver is removed the hook is forced upward. by a spring `(not shown), allowing the spring 3l to disengage from (not shown).

l the spring :hiciese to which'latter there is also secured a dialy (not shown) provided with linger holes. lWhen the dial is rotated lforward, a vcertain` number of teeth7 eorrr-spoluling to the digit called, are thereby advanced past the cani Si upon the end oli' the spring 27, but with no vetl`ect upon said spring. Vv'hen the dial is released it7 together with the impulse wheel, is returned to normal position by a. spring As each tooth passes the com 3? during" this haclu-*ard motion, the spring El? is forced out of engagement with 28 so as to open the bridge across the line.

The line switch C and master switch l.) are of the gei'lcral type disclosed in ,llritish Patent No. 26,301 ot 1906, and in the Vlifest- 1908'. As here shown, the line switch C consists essentiallyv ol a plunger. (not shown) attached to la plunger arm 3S,

and a magnet Bf.. lWllen the plunger arm is attracted by the magnet 3S) the plunger is forced into a bank of springs and y forces the springs 4.0, 4Q, lill and 4G intoconvtact with the springs 4l, v speetively.

43, l5 and 47, .rc- 'lhe magnet 39 is composed of four windings, a pull-1n winding 4S, a cul'- oli winding 4:9, a line winding 50 and anauxv iliary nflnding 5l.

The magnetic circuit of the windings eSlapd 49 is separate from that of the windingshfa) and 5l. The pull-in winding 48 is for the purpose of attracting "the plunger arm 238 to torce the plunger .into the bank. rlhc circuit ol the 'winding 178 is controlled by the calling subscribe-r through the medium of the line winding 50 and armature The 'winding 5l prevents the armature 52 :from 'falling back innuediatcly upon the deiiergi'fzation of the winding 50. The eut-oli winding 49 is provided for the purpose of holding the plunger arm 38 in an operated position and for operating the eut-oli' armature 53. lf the winding` dl) is energized while the armature and plunger arm 38 are in an operated position, both. the armature and plunger arm will be held in this position after the winding 4S is denergizcd; but if the winding 4:9 energized while the armature and plunger arm 38 are in normal position, only the armature will be operated, as the winding all) is not as strong as the winding 4S. Although only one set of 'Springs 40, 4i, 42, 473, 4.4i, 45. LG and .47 is shown, eaehline switch C is provided with a 'bank corn- "l` he plungers normally rest in locking engagement with a plunger shaft (not shown) and through the medium thereof are always held opposite an idle trunk terminal by the master-switch D.

The master switch D comprises a motor magnet 51 which operates the ratchet Wheel.

number of circuit-controlling relays. The

.master switch banks o and o are each provided with one individual segment for each trunk to which the switch C has access and a common segment. Each bank is provided with wipers 5G and 57 for keeping some one of the individual segments in electrical connection ivitli the common segment. By means of a suitable mechanical connection the rotary motion of the ratchet wheel 55 is transmitted to the plunger shaft to give the said sh aft an oscillatory motion and thus move the idle plun gers back and forth in' front of the bank terminals. To the plunger shaft there is also rigidly secured a cam' 5S having on its surface a number of circular openings which are engaged by the pin 59 on the armature 60. rhe openings in the cam 58 are so spaced that the pin 59 can engage an opening only when the plungers that are in engagementivith the plunger shaft are directly opposite the terminals of a trunk.

The secondary switch C is similar to the switch C except that its operating magnet has only one winding 61, which corresponds tothe pull-in Winding 48 of the switch C.

The master switch D is similar to the master switch D but lias only one bank of contacts. The relays G2 and 63 which are associated with the master switch. D are slow-acting relays-that is, relays which are sloiv to de'e'neigize after their circuits have been broken.

|The selectorA switch E is of the general type disclosed in United States Letters Patent No. 815,321, granted March 13, 19'06, to

Keith, Erickson and Erickson, but, as here shown, is adapted to operate in conjunction with a two-Wire system, z'. e., system in which there is no operating groiind at the substation for controlling the automatic switches. Among other details the selector comprises a set of wipers 6l, G5 and 66 carf ried upon a shaft (not shown) which has a vertical motion controlled by the vertical magnet 67, and a rotary motion controlled by the rotary magnet 68. The usual side switch, comprising the Wipers 69, 69, 71 and 72, is controlled by the privateA magnet 7 The operation of the switch is controlled by the calling subscriber through the medium of ythe doublenvound 1in-e relayt),

The release magnet 7e is normally disconnected from the battery by the separation of the springs 7 5 and 76, which springs are held out of engagement by the arm 7 7 as long as the switch shaft is in its lowest position.

The relays 78, 7 9 and S0 .denergize slowly after their energizing circuits have been broken. vThe ,selector is provided with the so-called` connector release, c., anism is restored immediately upon the energir/iation of the release magnet, rather than i by` its decnergiyiation, as shown in the said 55, tivo banks or contacts a and e and a l The connector 1l is of the type disclosed in United States Letters Patent No. 815,176, granted March 13, 1006, to Keith, Erickson and Erickson, but, like the selectors E and F, is adapted to operate in a twoovire system. Like the selectors the connector has a double- Wouiid line relay 81, vertical magnet 82, rotary magnet S3, release magnet Si, private magnet and a side switch. In addition, the connector is provided with a busy locking relay 8S, back-bridge relay S9 through which the called substation is provided with talking current, and airingei relay by means of which the generator L may be connected with the called line. The b nsy signaling machine consists of an vinterrupter 91 and an induction coil 92. The interrupted current through the nterrupter and primary Winding of the induction coil induces an alternating current in the secondary winding. Y

Having given a. general description of the apparatus, 14 will now. describe its inode of operation when the subscriber at substation A calls the substation A2, the number of which latter will be assumed to be 2220. ln order to call #2220 the subscriber at substation A first removes the receiver from the hook, then operates the dial once for each of the four digits. Vhen the primary circuit of the substation is bridged across the line conductors by the removal of the receiver from the'hook, it closes a circuit through the line Winding. 50 of the line switch C. This circuit extends from ground through the springs-93 and SM, line conductor 3l, substation springs 31 and 30, impulse spriugs'QS and 2 7, primary winding of induction coil 2l, transmitter 29:, line l,ind springs 95 and 96, through the 1vinding 50 and springs 07 and 0S to the battery lead 100, thence through battery ll to ground GL The winding 50, upon energizing, attracts the mechl its armature 52, which forces the spring 101 into engagement with the spring 03. rlhc`engagement of springs 101 and 03 closes an energizing circuit through the thence through the battery B to ground G.

The winding upon energizing, uttraets the plunger arm 38 und the cut-oit armature 53. lhe armature upon being attracted, :forces springs Si and 95 out of engagement with springs 93 and 963, respectively,thus opening the circuit of the winding 50. 'lhe armature 52 does not tall hack immediale'ly upon the deiincrgization of winding but remains held up hy the current flow!4 ing throughl the Winding 51. ltf'vhcn the plunger' arm 3S is attracted it 'forces thc`y plunger into the bank to press springs 40,

12, 41 and 46 into contact with the springs Ll1, 43, /115 and ,4r-7respectively. The plunger arm Si), in its operated position, also forces spring 10? into engagement with spring 10d, thereby shortleircuiting the winding 51,

ywhich causes the armature 52 to fall back slowly to open the circuit of the pull-in winding 11:8. lietore the armature 52 has time to fall back, however, the cutotwind ingl -1-9 is energized in `the following manner: then the lank springs flfl and 15 are pressed into contact they close a circuit extending 'troni ground G2 through said springs, over trunk conductor 105, and ihr-:nigh magnet G1 and springs 10G and 107 of the secondary switch C and through relay 108, contact point 109 and armature 11() to battery lead 100. The magnet G1, i'ipon energizing, attracts the plunger arm 113 and armature 114. "lhe plunger arm 113 operates to force the plunger into the bank lo press the springs 115x117, 119 and 121 into Contact with the springs 11G, 118, 120 and 12:2, respectively. operates to open the circuit of the relay 10.8 and close a locking circuit for the .magnet (51 through the springs 1.013 and 107iL and resistance 123 to the battery lead 100. The relay' 108, which is energized for an instant when the circuit is first closed through the magnet (31, closes a' circ-nit extending Jfreni ground 'G3 through the springs 111 and 112 and relay (53 to the buttery lead 100. r lhe relay G53, upon energizing, closes aY circuit exteiulingfrom ground G4 through the er mature 121-, contact point 125 (there heing ene such contact point 'for cach trunk to which the switch C has access), to the conductor 126,thence through the henk springs 12() and 119conductor 121'?, benl: springs 47 and 1G und winding #19 to the battery lead 1110. rihis circuit through the winding lil closed betere the Winding A1l-Sis dcenergized, as-before stated, and serres to holfVhe plunger hrm 35%' and urniature 53 in an operated position, l`he relay 13B is slonY to dciinergize after its circuit is broken, and consequently maintains this circuit through thewinding' 4.() until the selector 'E has time to close another circuitgas follows: 11n secures the'hanh 11.5 and 1.17 are i, A Y, .1

torce tinto contat i u the springs 116 and 11.8 hy the plunger .or ,the seceugliiry sivitci' Alhe arnuiture 1141` C an energizing circuit is closed 'through the line rclay() or the selector E. This circuity extends from ground G5 through the Winding 127 of the relay 70, side switch wiper 69a, trunk conductor 130, bank springs 11S, 117, 43 and 412, thence over the line conductor 31 `to and through substation A and back over linel conductor, bank springs ,410, Z11, 115 and 116, trunk conductor 129,

sideswitchnifiper G9 and Winding 128 of relay rto battery lead 100, TherelayTO upon energizing, shifts spring 132 outl 0 engagement with spring 133 and into contactwith spring 1311. The engagement of springs 132 und 134 closes. an energizing circuit. through the release relay 78. This circuit extends 'fronr ground G6 through springs 132 and 134- and relay 78 to battery lead 100. r1`he relay 78, upon energizing, shirtsI spring 13G out of engagement withv spring 135 and into contact with spring 137, and presses spring 138 into engagement' with spring 1.239. The engagement of springs 138 and 139 connects the ground G7 with the conductor 126 before the relay (121 has time to disconnect the ground G4. W'hen the conductor 12132- is grounded by the -operaition et the secondary switch C a guarding potential'is extended over the pri' rate normal conductor 140 to the connector bank contacts of the calling line, and a circuit is closed through the master switch relay 141. r-l`his circuit extends froml the eoruluctor 1262*, which is grounded, as pre riously described, through master switch bank contact 142, Wiper 57, common segment 113, and relay 1/11to battery lead 100. The

relay 111, upon energizing, closes a circuit through the relay 14A. The relay 14,4-, upon attracting its armature (SO, withdraws the iet pin 59 from the cam 58 and closes e Circuit i through the relay 11G and motor magnet b1. -llhe circuit through the ina-ffnet 54 extends l D b Le Jfrom ground (i8 through magnet 54, interrupter springs 117, contact point 148 and arn'iature (30 to battery lead 100. Uporthe closure 'of this circuit the ,motorn magnet he gins to operate in, 'a manner similar to that ot' ay buzzer to gire the ratchet Wheel 55 a step by step rotary motion. The motion of the wheel is transmitted to the plunger shaft, which operates to more. the idle plungcrs troni their positions in liront of the lrunh seized by the line switch. C. After the plungers have been moved a short distance the wipers 56 and 57, which are also attached to the plunger shaft, more oil the bank contacts corresponfling` to the trunk occupied by the switch C. When the wiper hi" leaves contact 142 the relays 14:1 and 1411- are denergized, but the armature .GO eunnot tall hack because the opening in the cam 58, which was formerly engaged with pin 5S), has passed out ci register therewith. Thus, the master switch will continue to operate uit `132 to disengage spring 134; and to engage spring 133. The relay 7 S is slow-.acting an does not have time to de'e'nergize during the momentary separation of springs 132 and 134. rlChe engagement of springs 132 and 133 closes a circuit through the private magnet relay 7 9 and vertical magnet 6 This circuit extends from ground Gr through springs 132 and 133, 136 and vertical magnet 67, and side switch wiper 2 to battery lead 100. Since the digit calle is 2, the vertical magnet receives two impulses over the circuit just traced, and operates to raise the shaft two steps, to carry the wipers to a position opposite the second row or level of bank contacts. As soon as the shaft leaves its lowestposition the arm 77 permitssprings and 7 6 to come `into engagement to provide the release magnet 74 with a battery connection. rlhe relay79, which is included in the energizing circuit of the vertical the first impulse, but being a slow-acting relay does not have time to deenergize between impulses. The relay 7 9, upon energizing, closes a circuit extending from ground through springs magnet 73 to battery lead 100. Aiter the last impulse is delivered to the vertical magnet` the relay 7 9 deonergizes and opens the circuit ot the private magnet 73, which in turn denergizes and permits the side switch to pass into second position. When the side switch wiper 72 passes from iirst tol secon position it disconnects the battery from the vertical magnet 67 through the rotary magnet 63.A extends rupter springs .156, rotary magnet 68, relay 80, contact point 157 and side switch wiper 72 to battery lead 100. Therotary magnet, upon energizing, operates to rotate the wipers one step to press down the private magnet armature and to open its own circuit at the -interrupter springs 156. When the rotary magnet circuit is thus opened the rotary armature falls bach, li the irst trunk, upon the contacts of which the wipers have just been rotated, is not busy the private armature follows the rotary armature and permits the side switch to pass Ato third position. lt the iirst trunk is already busy, however, thefprivate wiper 65 inds the iirst bank contact grounded, and thus closes a circuit extending through the side switch wiper 71, contact point 158 and private magnet 7 3 to battery lead 100. The private mag net thereupon encrgizes and locks the side switch in second position. W'hen therotary armature permits the interruptor springs to again engage, the rotary magnet energizes a second'time to advance the wipers a second step. The wipers will thus be advanced stepby-step until the private wiper 65 en'- gages a non-grounded contact of' an idle until the next opening in the cam passes under the pin GO, when the said pin drops into this opening, locking the shaft against further rotation, and the armature (SO disengages from the contact point 14S, thus opening the circuit of the-magnet 54 and' relay letti. lf the next trunk after the one seized by the line switch C has been busy the wiper 57 would have found the corresponding contact guarded, and would have nuiintaiued the circuit of the relays 141 and 1-1-1 while the next opening in the cam was passing under pin 59. Thus, the master switch would have continued 'to advance the pl'uugers past-the busy trunk. The relay 146, the circuit of which is closed during the time the master switch is rotating, operates to disconnect the battery 'from the line winding 50 of all switches that are controlled by the master switch D, and to conneet the busy signaling machine l with all idle lines through their line windings 50 and springs 9G and 95. Then the bank springs 121 and` 122 are pressed into engagement by the plunger of the secondary switch C circuit is closed extending from ground Gr through the said springs, masterswitch bank contact 227, wiper 149, seg` nient 150. and relay 151 to battery. The re lay 151, -upon energizing, closes a circuit through relay 152, which in turn unlocks the plungedr shaft and causes the master switch D to advance the idle plungcrs to an idle trunk in the same way in which the relay 1li caused the operation of the master switch D. While the master switch D is operating, the armature 110 is separated from the contact 109, thusdisconnecting the battery from thetidle seconda-ry' switches to prevent their operation while their plungeis are in motion. In its operated position, the armature 11() also opens the circuit of relay 62. The relay 62 is a slow-acting relay and does not have time This circuit to denergize it the master switch D does'not have to pass over busy trunks. It', however, a number of busy trunks are to 'be passed over, the relay 62 denergizes and connects the ground x1 with the contact 153 of the auxiliary bank @het the master switch D. This ground on the contact 153 prevents the master switch l) t'roin stopping, with the plungers in position to engage this trunk, while the master switch D is rotating.

The foregoing operations take place irnmediately upon the removal of the receiver at the calling substation and before the impulses are sent in for the iirst digitot the desired number. When the calling device is operated for the iirst digit 1(2) the impulse springs 27 and 28 are separated twice morIhe sepa-ration of springs 27 and 28 breaks the energizing circuit of the line relay 7 0 of the first selector E. rEhe relay 7 O, upon 'denergizing, permits spring 137, relay 79,

151i and 155 and privateand closes 'a circuit' trom ground G5 through inter magnet 67, is energized by trunk, whereupon the private magnet deenergizes and allows the side switch to pass to third position. TWhen the side switch leaves second position the wiper 72 breaks the operating circuit ol the rotary magnet.

The relay Ut) energized in series with the y rotary magnet 68 and, being a. slow-acting relay,remains energized for a short time after the rotary magnet is energized tor the last time. Thus, at the inst-ant the side switch passes to t/hird position, the seized trunk is provided with a guarding potential exteiiding from ground Gu through springs 159 and 160 of relay 80, contact point 161, side switch wiper 71 and shaft' wiper 65 to the selector private baul; contacts. the side switch wipers 69 and 70 pass from second to third position the relay 70 is disconnected trom the lineand the line con niietion is extended through the sha'tt wipers 6i and 66 to the selector 1", energizing the relay 162 in the same manner that the relay 7 6 ot t-he selector 1G was energized. The relay 162, upon energizing, closes a circuit trom ground through springs 16S-S and 161 and relay 165 to battery lead 100. The relay 165 thereupon energizes and supplies a new guarding ground to the private bank contacts of the first selectors. Also, as soon as the rrelay 8O ot the selector E falls back a new circuit 'is closed through the release relay 78. This circuit extends from ground G13 through side switch wiper 166 ot the second selectin' l?, springs 167 and 168 ot 'relay 165, conductor 169, private wiper 65,

side switch vt'iper 71, contact point 161, springs 166 and 170 et relay 80 and through relay 78 to batter f had 100. rThis circuit is closed before the relay 78 has time to deeiiergize aitter its formerv circuit is opened by the dcnergization o1 therelay 70. It is thus evident that the relay 78 must be slower than the relay 80, the function ot' which is to provide a guardingl potential` for the seizedy trunk between the time that the side switch otthe selector E passes lo third position and the time that the relay 165 ot' the selector i'i f energizes. rthe second selector 1V is now in position to receive impulses for the second digit, and operates in response to these digits to extend the connection to the connector H over the conduct-ors 171 and 172, in the saine manner as the selector IG. 1iVhen the connection is extended to the connector theline relay 81 is energized in the saine manner that thc relays 162 and 70 ot' the switches ii` and E were energized when the connection was extended to their respective switches. The relay 81, upon energizing, closes a circuit through the release relay 87, Which operates toclose a new circuit through the relays 165 and 78 ot the selector switches. lThis circuit extends tronil ground GM through side s wilch wiper 'springs- 176 and 175, coiuluctoij Etta-istintiwiper-177,

When

morena side switch wiper 178 and springs1'80 and 179 to point 181. From point 181 one branch of this circuit passes through the relay 165 to battery, and another branch passes line relay 81 ot the connector is denergized.

twice momentarily. Each time the relay 81 deencrgizes a circuit is closed pxtending from ground G15 through springs 182 and 188, 181 and 185, vertical magnet 82, side switch wiper 186 and private magnet relay 86 to battery lead 100. The vertical magnet receives two impulses over this circuit anti operates to raise the shaft and wipers two steps. 'The private magnet relay 86 .is energized by the first impulse to the vertical magnet, and remains in its operated posit-ion until atter the last impulse is delivered. In its energized'position the relay 86 closes a circuit extending 'from ground G1 through springs 187 and 188 and private magnet 85 to the battery lcad 100. Whenvthe private magnet relay 86 denergizes after the last impulse is delivered to the vertical magnet it breaks the circuit oty the private magnet' 85, which latter inI turn deenergizes and al lows the side. switch to pass tirsecond position, 1V hen the side switch wiper 186 reaches second position it connects the rotaryrL magnet 83 with the battery lead 100 through the private magnet relay 86. `When the calling device is operated for the last diget (O) the relay 81 denergizes ten times, cach time closing a circuitthrough the rotary magnet 83.

This circuit extends from' ground (im through springs 182 and 183, 184:*-

and 185, 189 and 190, rotary `magnet 83, side switch wiper 186 and rela-y 86 t-o battery leal-106. Since the digit called is O, the rotary magnet receives ten impulses oit this circuit and operates to rotate the wipers ten steps onto the tcrniinals of the line #2220. rl`he privato magnet relay 86 is energized by the tirst one ol this series ot' impulses and again closes thc circuit of the priva-te magnet 85. The relay 86 denergizes a'fteijtlie last impulse. is delivered to the rotary inagnet, and opens the circuit of the. private magnet 85, which thereupon allows its arma.-

ture to fall back and trip the side switch The movel'i'oui sc'eouil to third position. ment ot the sidc switch wipers 191 and 192 to third position extends the connection through the wipers 193 and 101; to the line ol 'thccallcd substation. -lNhen theside switch wiper lvengages its third-,position contaet'pointit establishes a guarding po- "t'c'ntial at thc connector private bank coin tacts ot the called line, and closes a circuit the called subscriber through the cut-oft winding 19o ot' the line switch C2. This circuit extents-f l'roin Ground GU through side switch ivi 9er 195, shrines D A C 19,7 and'19S, private wiper 199 and bank contact with which it is in Contact, and winding` 196 to the battery lead 109. The winding 196 upon energizing, attracts the arn'iature 299, which operates to disconnect the'switch C2 from the called line and to connect the line conductor '291 with the connectpr bank contact which is ,I engaged by wiper 193. lYhcn the side switch wiper 1S() engages its third-position contact point a circuit is closed extending from greun-ddtils through interruptor 203, springs 204 and 205, ringer relay 90, side switch wiper 186 and relay 86 to battery lead 190. The relay 90, upon energizing, disconnects the calling and called lines and connects the ringer generator-L with the called line to ring the bells 22S. Sincecthe circuit ot the ringer relay includes the intcrrupter 2023, the said relay is energized only intermittently so as not to ring the called subscriber continuously. Vtlhen removes his receiver, or as soon thereafter as the ringer relay deenergizes, itl it energized at the time, the called substation is provided with talking current over a circuit ixtending from ground G through side switch wiper 195, winding 229 of the relay S9, ringer relay springs 20G and 297, side switch wiper 1927 sliait wiper 1li-l, line 202, hook switch springs 298 and 299, impulse springs, transmitter and primary winding ot' thc subst-ation A2, line 201, shaft wiper 193, sideswitch wiper 191, ringer relay springs 210 and 211- and winding 212 of the relay S9 to battery lead-199. The relay 89 thereupon cnergizes and separates the springs 29-1 and 205, thereby opening the circuit oi' the relay 90 to prevent its further energization after the called subscriber has answered.

After the conversation is completed the release of the central olli-cc switching apparatus is initiated by the restoration ot' the receiver at the calling substation. lilien the springs 30 and 231 are separated by the replacing ot the receiver on the hook at the calling substation they brcakthc energizing circuit of the line relay 81 of the connector H. The relay 81, upon deiiuergizing. permits the spring 182 to disengage the s lning 213, thus breaking the 'circuit ot the release relays ST, 165 and TS ot the switches 1l, l" and E, respectively.` t is evident that after the side switch wiper .174 passes to third position the holding ground ot .the selector release rela-ys 1(35 and 78 is shitted 'ifi-om ground G* to ground G through the sl'irings 213 and 182, so that thedenergization ot the relay 81 opens the circuit ot the selector lrelease relays, as well as thatfot' the connector. 'he release relays7 upon dencrgizing, close. the circuits of the release magnets ot their respective switches. The circuit of the release magnet 84 of the connestor H extends from ground G15 through the springs 182 and 183, 1.8/1 and 214, magnet Se and ott' normal springs 215 to battery. The reieave circuit of the first selector E extends troni ground GG through springs 132 and 133, 1313 and 135, magnet 74 and otl' normal springs 75 and 76 to battery lead 100. The release circuit of the selector F is similar to that of the selector E. The various release magnets5 upon energizing, cause the mechanisms of their respective switches to be restored to normal position. Vllhen the shaft of each switch reaches its lowest position it opens the circuit o its release magnet by operating the off normal springs. then the release relay 7,5 of the selector E denergizes', besides closing the circuit of the release magnet 7e it Vopens the circuit et the winding 49 of the line switch C by allowing the springs 138 and 189 to disengage. r1`he deenergization 01: the windingl e9 allows the plunger of the `line switch C to restore to normal position, 'thereby disconnecting the calling line from the secondary switch C and breaking the cirl cuit ofthe magnet 61. rEhe magnet G1, upon denergizing, allows the secondary switch to berestored, and all the apparatus used in the connection is ready for another call.

Returning now to that stage o' the opera tion when the connector wipers have been advanced to the contacts ot the desired line, and before the private magnet relay has had time to denergize, it will be explained how the calling subscriber is given nal in case the called line is already in use. From the`foregoing description it is evi'- dcnt that whenever a line is in use there is a ground potential upon its contacte in the private bank of the connectors which have deenergizes'aijui allows spring- 188 to engagefspring 2lb' with the private wiper 199 resting on the grounded contact ot a busy line, a circuit is closed extending 'from said grounded .contact through .wiper 199, .springs 19S and 197, winding 229 ot' relay 89, ringer relay springs 20G and 207, side switch wiper 192, contact point 217, springs 216 and 188 and private magnet 85 to battery lead 100. The spring 188 engages the spring 216 be- 'tore breaking contact with the spring 187. rl`he private magnet thus remains energized, lockingthe side switch in second position, l and at the same time the' relay 89 is enered by the current in the coil .229. The rr f 89, uponenergising, closes a circuit tln'- .ugh the locking rela-y S8. `This circuit extends 'trom ground C"G through springs 18T and 218 ot relay 8&3, springs 219 and 221i, relay S8 and springs V221 and 222 to battery lead 190. 'l`he relay SS, upon energizing, l disconnects the rotary magnet 8311-0111 the the busy sig-.

access to it. 'When the private magnet relay impulso spring 183, shifts the holding cipy .springs 2l() and 2li, condenser 226and thence over the heavy conductors shown in Figs. 2 and l to and through substation 1i and back over the other side of the line, through one winding ot' the relay 8l to ground, and thence through the battery B' to the starting point. The calling substation will coutume to receive the busy signal until the receiver is restored to the switch hook, when thearelease of the" switches will 4take place in the same manner as when a complete connection is established.

Having givena description of the operav tion of the system I will now explain the disand secondary switches.

Each group of primary switches is usually provided with ten trunks and .thesecondary switches are divided into ten gro-upsn Each tribution of the trunks between the primary `ofthe ten 'trunks leading from a primary group leads to a switch 1n a different seo' ondary group. ini Fig. 5 are shown diagrammatically the trunk terminals of twelve groups of primary switches C, and tens secondary groups each consisting oi' 1twelve secondary switches C. rlhe connections oit' all ten trunks ot" the first three primary groups are shown, while only two trunks in each of theother groupsN are represented.

'As herein represented, the lirst trunk from theiirst primarY group leads to the irst switch of secon( ary group #1, the second trunk leads to the first switch of secondary group #lieto The lirst trunk of the primary group #il leads to the second switch of secondary group yil:6,.the second trunk leads to the second switch in the irst secondary group, etc. By means of the table shown in 'Fig.`f l, the connection of any trunk may be determined. The number abo've each vertical row 'oil squares indicates the number ot a secondary group, and the number at the left ot each horizontal row indicatesthe number of a primary group. In each small square the upper left hand figure represents the number of a primary group, the upper right hand ligure represents a trunk in that group, the lower left hand, figure represents the secondary' group, and .the lower right hand figure, the switch in that group to which the trunk is connected. To give an example of the use of the' table, the first square in the first row would be read as ollows: From the iirst primary group the irst' trunk leads to the first switch of the first secondary group. llhesecond square signifies that the second trunk from the f `lirst primary group leads to theyhrst switch in the second secondary group.}\ Frmn an itispectwn of the table it 1s evident thatthe upper left hand ligure and the lower right y different order in each row. lilith the trunks distributed :according to this table, it the plungers' of all oli the first ten primar groups are placed in .trent oi- 'the trans: leading to the same secondary group, and then each primary master switch is rotated one step, the plungers of no two primary groups will then be in position to engage trunks leading to the same secondary group. As shown, the table applies to only twelve primary groups, lbut may be easily extended 'to apply to any number. To extend the table all that is necessary is to add one horizontal row of ten squares for each primary group and number the rows consecutively, placing the number outside at 'the left of 'the row: The number at the left oi. the row is then placed in the lower right and upper lei't hand corners of each square. The number which appears above the vertical row in which each square lies is' placed in the lower left hand corner. The numbers in the upper right hand corners of` the squares in row No. 13 should be the same as those in row No. 3; the upper right hand numbers in row No. 1liv are the same as the corresponding numbers in row No. Il, etc. in other words, the upper right hand numbers in the corresponding squares of every tenth horizontal row are the Same. W ith the table as here shown, the number of the individual secondary' switch to which a primary trunk is connected is the same as the number of the primary group from which the trurk leads; It is not essential to the' principles oi my invention, however, that the trunk lead to this particular switch, Ias the same result will be obtained if the trunk leads to -any switch in the group designated by the lower lill) lll) lo'lt hand figure in the square. 'llhe object in connecting the trunk to a particulariswitch in the secondary group is that a more sys; tematic arrangement is thereby obtained than heretofore.

The contacts of the auxiliar-y bank a ot the primary master switch are distributed Iin the same manner as the trunk lines. Each bank vcontact of the bank a. is connectedk to the contact of the relay 62 belonging to the 'lhe table shown in Fig. 4; may be used in determining the connection of the master switch bank contacts. Since there is only one relay 62 for each secondary group, thei` lower right hand figure in each square is not, used for determining the connection ofthe master switch bank contacts. As an example of the use of the table in connection with the master switch bank, the figure 8 in-` the upper right hand corner of the third square in the top row signifies that the third contact in the bank a of the i'irst primary group, designated by the upper left hand figure, is connected to the contact of the relay 62 of the third secondary group, designated by the lower left hand figure 3. Fig. 6 shows diagrammatically the connection of a part of the master switch bank contacts.

From the foregoing it will be seen that l distribute the calls evenly, or more nearly so than heretofore, between the diierent groups of secondary non-numerical trunking switches. Furthermore, l provide a greaternumber of switches in 'each Vsecondary grouptlian there are trunks in each primary group. In this way theprimary groups are greater in number than the sec` ondary groups, the number of trunks leading to each secondary group being the same in number as the total number of primary groups. Thus the first selectors are all common to all the subscribers, any subscriber in the exchange having access to any particular rst selector; and with my improved arrangement of the trunks between the primary and secondary switches', successive calls from as many different groups'of subscribers are not concentratedui'n'one and the same group of first selectors, but to the contrary are distributed iidifierent groups of first selee/tors, thus equalizing` the load and preany particular `With my improved arrangement there are as many preselected trunk lines ready and waiting at all times as there are groups ofsubscribersthat is to say, as there are groups of primary switches-and cach of these trunk lines, or some of them, leads to a different group of secondary switches, even though the master switches are all in the saine position. With the old arrangement the condition of the trunks between the primary and secondary 'switches was such that a call from one group of primary switches would be directed to a certain group of secondary switches` and succeeding calls from other groups of subscribers would, if all the master switches were in the saine position, all be directed to the same group of secondary switches, until this particular group of secondary switches from group that group, which trunk leads to group #d was rendered entirely busy, or filled up, so to speak, thus concentrating the calls in one group of secondary switches. Withmy improved arrangement, and assuming that -no subscribers have called, a subscriber calling,

from the first grou (ql-,t1 Fig. 5) will get the iii-st trunk leadiiig to the first group of secondary switches; then a subscriber calling .#2 'will get the first trunk of* of secondary switches; then a subscriber calling from group :p53 of the primary switches will get the first truigk line leading "from that group, which trunk line, however,

leads to group #4 et the secondary switches. dn this way, and even when the master iswitches of the different primary switchesire all in the same position, successive calls are then distributed to different groups of secondary switches. successive calls from the different groups .of priniaryswitches could only be concentrated in a certain groupcfsecondary switches by reason of the simultaneous arrival of the different masterswitches of the primary groups at the terminals "ci the diferent trunks leading to the articulan-groupl of secondary switches, an this, et course, -is not liable to occur. With my improved arrangement, and even assuming that the mast-er switches of the primary groups are all in first position, successive calls from the different primary groups will be distributed to vthe dierent groups of secondary switches, so that n0 secondary group will receive more than one of said calls. ln this way the traic is evenly distributed and an overload on anyparticular group of rst selectors is .not likely to occur. Thus when av subscriber of one group calls, the master switch or" that group is operated to pick out or preselect another trunk for the next calling subscriber in the same group, but the master switches for the other gronpsare not disturbed. i

Referring to Fig. 5 it will be seen that the arrangement here shown constitutes what may be called a traffic distributer. rlfhe arrangementl is such that the calls are automatically distributed indifferent secondary groups. There are as many trunks termi- Obviously, therefore,

ics

hating in each secondary group as there are primary groups, and there are as many trunks leading from. each primary group as there are secondary groups. The trunks of any secondary group, or at leastsome of them, are given unlike, or dissimilar positions in as many diii'errent primary groups.

given various aufl olifferent posit? in the remaining primary groups. ln tliis Wu-y tbe trunks 'Wliicli occupy like or similur pour tions in tlie different primary groups arranged to terminate at es many dillierent secondary groups. Tinus, as stated, tbe ai rangement tends to equalize the loud anrl distribute tbe traffic more orenly between tbe (iliil'erent secondary groups.

lllliat l claim :is my invention isz-- l ln telephone system, a plurality of subscribers lines, u plurality oi groups of primary non-numerical trunlring switches, a plurality oli lgroups of secondary non-numerical trunlringn switches, trunks extending from the primary groups to the secondary groups, tbe number of primary groups be ing' greater than tbe number of secomlsry groups, and. tlie number of trunks leading to each secondary group being the seine us tlie number otl primary groups, und, nieuns ttor controlling saitl primary non-numerical switches over two sides oi a subscribers line in series.

2. ln a telephone system, u, plurality of subscribers lines, aI plurality olf groups oi" primary non-numerical trunling switcbes, s ilurality of groups of secondary non-nu mericel trunking switches, trunks leading from tlie primary groups to tlie secondary groups, tbe number of trunks leading' from each primary group being; tbe same :is tbe number of secondary Lgroups, tbe number ot trunls leading to each secondary group being tbe as the number of primary' groups, and tlie number olE primary groups bei ng greater than the number oi? secondary groups, anol means for controlling said prr mary non-numericsl switches over two sides of a subscribers line in series,

8. ln a telephone system, e plurality ot subscribers7 lines, n plurality of groups of primary non-numerical trunlring switches, s. plurality oi' groups of secondary non-numerical trunking switches, trunks connecting tbe primary groups with tbe secondary groups, tbe number of primary groups locing fliilierent from tlie number of secoiulary groups, tlie number of trunks leafling from eucli primary group being tlie saine as tbe total number of secondary groups, anni tlie -nurnber ol? trunks lending to euch secondary group beingn the sume tlie total number of primary groiuis, und menus for controllinoF sfiifl primary non-numerical switches oi'elr two sirles of u subsoribcrs line in series.

al. ln u telephone n plurality oli groups of primary non-numericul trunlring switches, a plurality of groups of secoiulury non-numerieul t-runkiug su'itclies,unl trunks connectingn the primary groups with tbe sec onflsry groups, tbe trunks terminating; in any particular second-ery group bei given (li linllzi poitiow: in tbe tliileonl; primary groups.

moines ln .fi telephone system, plurelity oit groups of primary nonuiumcriosl trunliing' switches, a plurality of groups of secondary' nonnumerical trunlring switches, and trunks connect-ingw tlie primary groups With the secondary groups, the number ot' pri mary ,groups beingl greater liban tbe number of secondary groups, and the trunks Wliicb. have similar positions in the primary groups, or somo of' tliein, being arranged to terminate it their other eiuls in dillierent secondary groupsn G. ln a telephone system, a plurality or groups of primary non-numerical trunking switches, a plurality of groups ol,t secondary noinnumericul trunliing switches, and trunks connecting the primary groups with the secondary groups, tbe number olf primary Lgroups being ,greater tlian tbe number or" secoiulary o'roups, tlie trunks tern'iinating in any seconary group being the suine in niunber as the total number of primary gruppe, o. number of trunks in escli secondary group equal to tbe total number of secondery groups being` given dissimilar positions in, as runny dil'eient primary groups, snol the remaining trunks oi each secondary group being given positions in the remaining primary groups similar to tlie positions that certain other trunks of tbe same seconclary group are given in other primary groups.

l'. Ln s telephone system, s plurelity of subscribers lines, e plurality oit groups of primary nonnuinerical trunlriizip,` switches, a plurality olf groups of secondary non-nu merical trunlring switches, trunks extending from tlie primary groups to tbe secondary groups, tbe number oi? primary groups be inge, greater then the number ol secondary groups, und tbe number of trunks lending 'to each secondary group being tbe same as the number of primary groups, means for controlling1 ssicl primary non-numerical switches over two sides of a subsoribers line in series, und e muster switch for euch primary group, euch muster switc-li, when all are in tbe same position, beine; in selectivo relation to a secondary group different iroin those of other master switclies.

8. .ln u telephone system, a plurality of subscribers lines, a plurality of groups of prinuiry non-numerical trunlring switches, a plurality of groups of secondary non-numericaltrunkingi,- switches, trunlrs leerling from tbe primary groups to tbe secondary groups, the npinloer oi trunks leerling from eucli primary ,group beingu tlie sume as the Ynumber of secondary lo roups, tbe number ot ",trunlrs lending to each secoiulury group be ingr the same as the number of primary 4groups, incl tbe number oli primary `irroups being peuter tliiin the number oli secondaryg'roups, means :tor controlling` suiifl primary non-numerical. switches over tufo sides of si lll? :morgana` subscribers line in series, and a master switch for each primary group, each master switch, when all are in the same position, being in selective relation to a secondary group different from those of other master switches.

9. n a telephone system, a plurality of subscribers lines, a plurality of groups of primary non-numerical trunking switches, a plurality ot' groups ot secondary non-numerical trunking switches, trunks 4connecting the primary groups with the secondary groups, the number of primary groups being ditlerent from the number of secondary groups, the number ot' trunks leading from each primary group being the same as the total number of secondary groups, and the number of trunks leading to each secondary group being the same as the total number of primary groups, means for controlling said primary non-numerical switches over two sides of a subscriber-s line in series, and a -master switch for each primary group, each master switch, when all are in the same position, being in selective relation to a secondary group dilterent from those of other master switches.

10. In a telephone system, a pluralit ol" groups of primary non-numerical trun ring switches, a plurality of groups of secondary sion-numerical trunking switches, trunks connecting the primary groups with the sec ondary groups, the trunks terminating in any particular secondar group being given dissimilar positions in t e dii'erent primary groups, and a master switch for each primary group, each master switch, when all are in the same position, being normally in selective relation to a secondary group di ferent trom those of other master switches.

ll. In a telephone system, a plurality of groups of primary non-numerical trunking switches, a plurality of groups ot1 secondary non-numerical -trunking switches, trunks connecting the primary groups with the secondary groups, the number ot primary groups being greater than the number oit secondary groups, and the trunks which'have similar positions in the primary groups, or some ot them, being arranged to terminate at their other ends in diierent secondary groups, and a` master switch for each primary group, each master switch, when all are in the same position, being in selective relation to a secondary group diiierent from those of other master switches.

12. ln a telephone system, a plurality of groups of primary non-numerical trunking switches, a plurality of groups of secondary non-numerical trunking switches, trunks connecting the primary groups with the sebondary groups, the number of primary groups being greater Athan the number of secondary groups, the trunks terminating in anyjsecondary groupfbeing the same in number as theY total number of primary groups,

a number" bf trunks in each secondary group equal to the total number of secondary groups being given dissimilar positions in as many different primary groups, and the remaining trunks of each secondary group being given positions in the remaining primary groups similar to the positions that certain other trunks ot the same Secondary group are given in other primary groups, anda master switch for each primary group, each master switch, when all are in the same'position, being in` selective relation to a ,sec-V ondary group different from those of other master switches.

13. In a telephone system, a 'plurality of subscribers lines, a plurality of groups of primary non-numerical trunking switches, a

plurality of groups ot secondary non-numerical trunking switches, trunks extending from the primary groups to the secondary groups, the number of primary groups being greater than the number of secondary groups, and the number o trunks leading to each secondary group being the same as the number of primary groups, means for controlling said primary non-numerical switches over 'two sides of a subscriber-s line in series, trunk linens leading from said secondary groups, and' a iii-st selector for each trunk line, whereby each first selector is common to all ot the primary groups le. ln a telephone system, a plurality of subscribers lines, a plurality of groups of primary non-numerical trunking switches, a plurality of groups of secondary non-nu-v merical trunking switches, trunks leading from the primary groups to the secondary groups, the number of trunks* leading from each primary group being the same as the number ofsecondary groups, the number of trunks leading to each secondary group being the same as the number of primary groups, and the number of primary groups being greater than the number of secondary groups, means for controlling said primary nonnumerical switches over two sides of a subscribers line in series, trunk lines leading from said secondary groups, and a first seleccor for each trunk line, whereby each irst select-or is common to all` of the primary groups.

15. ln a telephone system, a plurality of subscribers lines, a plurality or" groups of primary nonnumerical trunking switches, a

plurality of groups ot secondary non-nu merical trunking switches, trunks connecting the Aprimary groups with .the secondary groups, the number of primary groupsibelosy mg dilterent from the number of secondary groups, the number of trunks leading from each primary group being the same as the total number ot'seeondary groups, and the number of trunks leading to each secondary group being the same as the total number of primary groups, means for controlling said las' primary nonsnnmerical switches oyer two sides ot' a subscribefs line inV series, trunk liuc-s leading from said secondary groups, and a iirst selector for cach trunk line, whereby each first selector is common to all ot the primary groups.

lli, ln a telephone system, a plurality ot groups ot primary non-immerical truuking switches, a plurality oli groups ot secondary non-mimcrical trunking switches, trunks connecting the primary `groups with the secomlarjyf groups, the trunks terminating at "an-y particular secondary group being given groups groups being greater than the number dissimilar positions in the dill`crent primary groups, trunk lines lauling trom said secondary groups, and ar lirst selector for each trunk line` whereby each tirst selector is common to all of the primary groups.

l?. ln a telephone system, a plurality ot groups ot primary non-numerical trunking switches, a j ,ilurality of groups of secondary non-murierical trunking switches, trunks connecting the primary `groups with the secondary' groups, the number ot' primary being greater than the number ot secondary groups, and the trunks which hare similar positions in the primary groups, or some of them, being arranged to terminate at their other` ends in ditterent secondary groups, trunk lines leading from said secomlary groi'ips, and a first selector tor each trunk line, whereby each first selector is common to all ol` the primary groups.

1S. ln a telephone system, a plurality ot groups ot primary non-numerical trunking switches, a plurality oi groups ot secondary non-numerical trunking switches'. trunks connecting the primary groups vwith the secondary groups, the number of primary ot' secondary groups, the trunks ttuminating` in any secondary group being the same in number as the total numberofprimary groups, a number of trunks in each secondary group equal to `the total number of secondary gro-ups being given dissimilarpositions in as many di florent primary groups, and the remaining trunks of each secondary group being given positions in the ren'iaining primary groups similar to the positions that certain other trunks ot the .saine secondary group are given in other t limary groups, trunk lines leading 'from said secondary groups. and a tirst selector for ach trunk line. whereby each first sclcctor is common to all o'` the primary groups.

if). ln a telephone system, a plurality ot groups ot primary iiounuuicrical trunking switches, a plurality of groups ot seconda ry non-numerical trunking switchestrunks eX- tcmliug from the primary groups to the secA ondary groups. the number oi primary groups being greater than the number of I secondary groups, and the number of trunks leading to each secondary group being the .same as the number ot primary `gro-ups, means including selectors and connectors for extending connection -from the secondary groups in th'c direction ot the called subscribers. and means for contiiolling said selector-s and connectors over the two sides of the line circuit in series.

20. ln a telephone system, a plurality of groups of primary non-numerical trunking switches, a plurality' o'l groups of secondary non-nu1nerical trunking switches, trunks leading trom the primary groups to the secondary groups, the nmnbcr of trunks leading from each 4as the number of secondary groups, the number o't'trunks leading to each secondary group being the same as the number ot primary groups, and the number of primary secondary groups, n'ieairs including' selectors and connectors for extending connection from the secondary groups in the direction of the called subscribers` and means for controlling said selectors and connectors over the two sides of the line circuit in series.

21. In a telephone system, a plurality of groups of primary non-numerical trunking switches, a plurality oi groups of secondary non-numerical trunking switches, trunks connecting the primary groups with the secondary groups` the number of primary groups being different from the number oit secondary groups, the number of trunks leading `from each primary group being the same as the total number of secondary groups, andthe number of trunks leading to cach secondary group being the same the total number of primary groups, means including selectors and connectors for extend ing connection from the secondary groups in the direction of the called subscribers, and

nectors over the two sides ofthe line circuit in series.

Q0. ln a telephone system, a plurality of groups ot primary non-numerical trnnking switches, a pluralityv of groups of secondary non-numerical trunking'. switches, trunks connecting the primary gropps with thel secondary groups, the trunks terminating in any particular secondary group being given dissimilar positions in the different primary groups` means including selectors and connectors tor extending; connection from the sccoiu'lary groups in the direction of the called subscribers. and nieans for controlling said selectors and connectors orcr thc two sidesot the line circuit in series. y

23. 'ln a telephone system. a plurality ot groups ot primary non-numerical trunking switches. a plurality ot groups ot secondary non-numcrical trunking switches, trunks .connecting the primary groups with the secprimary group being the same means for controlling said selector and con groups being greater than the number ofliti-tl :monetai have similar positions in the primary Urouis' or some of them beine arranged 2:: a i #-1 b to terminate at their other ends in different secondary groups, means including selectors and connectors for extending connection from the secondary groups'in the direction of the called subscribers, and means 'or controlling said selectors and connectors over thetwo sides of the line circuitin series.

Q4. in a telephone system, a plurality of groups of primary.non-numerical' trunking switches, a plurality of groups of secondary "non-numerical trunking switches, trunks connecting the primary groups with the secondary groups, the number of primary groups being greater than the number ot, `secondary groups, the trunks terminating -tin any secondary group being the same/1n number as the total number of primary groups, a number of trunks in each second- `Vary group equal to the total number f/,sec- -ondary groups being given dissimilarypositions in as many different primary groups, and the remaining trunks of each ,secondary group being given positions'in thfrernaining primary groups similar to positions that certain other trunks of the same secondary group are given in other primary groups, means including selectors and con-A nectors for extending connection from the secondary groups in the direction of the called subscribers, and means for controlling said selectors and connectors over the two sides' of the linecircuit in series.

25. in a telephone system, a, plurality of groups of primary non-numerical trunking switches, a plurality of groups of secondary non-numerical trunking switches, trunks extending from the primary groups to the secondary groups, the number o primary groups being greater than the number of secondary groups, andthe number of trunks leading to each secondary group being the same as the number of primary groups, trunk lines leading from said secondary groups, and means for controlling the switches of the primary groups over metallic line circuits.

2G. In a telephone system, aplurality of groups of primarynon-numerical trunking switches, a plurality of groups of secondary non-numerical trunking switches, trunks leading from the primary secondary groups,'the number of trunks leading,r from each primary group being vthe same as the number of secondary groups, the number of trunks leading to each secondary group being the same as the number or pri.

mary groups, and the. number of primary groups,l being greater than the number of i'secondery groups,-

leading from each primary groups to the truuk lnesleading from. v

said secondary groups, and means for controlling the switches of the primary groups over metallic line circuits.

27. In a telephone system, a groups of primary non-numerical trunking switches, a plurality of groups of secondary non-numerical trunking switches, trunks connecting the primary groups with the secondary groups, the number of primary groups being different from the number of secondary groups, the 'number of trunks group being the same as the total number oi' secondary groups, and the number of trunks leading to each secondary group being the same as the total number of primary groups, trunk lines leading `from said secondary groups, and means for controlling the switches of the primary groups over metallic line circuits.

28. In a telephone system, a plurality of groups of primary non-numerical trunking switches, a plurality of groups of secondary non-numerical trunking switches, trunks conv necting the primary group'swith the secondary groups, the trunks terminating in any particularsecondary group being given 'dissimilar posit-ions in the different primary groups, trunk lines lea ing fromsaid secondary groups, and mea s," foriA controlling the switches of the primar "groups over metallic line circuits. /f' 1,

Q9. .ln a telephone system, ,a plurality of groups of primary nonnumerical trunking switches, a plurality ofy groups of secondary non-numerical trunking suf'itches, trunks connecting the primary groups with the secondary groups, the number of primary groups being greater than the number of secondary groups, and the trunks which have similar positions in the primary grpups,\or some of them, being arranged to terminate at their other ends inl diii'erent sedondary groups, trunk lines leading from "'aid secondary groups, and means for c ntrolling the switch-es of the primary groups over metallic'line circuits.

30. In a telephone system, t groups of primary nou-numerical lranking switches, a plurality of groups of secondary non-numerical trunki ng switchesl trunks connecting the primary groups Witlnthe secondary groups, the number of primary groups being greater than the number of Asecondary groups, the trunks terminating in any secondary group being the sume in number as the total number oi primary groups, a num- -ber ot trunks iu each secondary group equal to the total -number of secondary groups being given dissimilar positions in as many di'tierent primary groups, 'trunks ot each secondary group being given positions in the remaining primary groups similar to the positions that certain other trunks. he same secondary group are and the remaining othsertiraarr stesi-issuers' liess plurality of' i fait 

